A fuel cell is a device which generates electrical energy by converting chemical energy, derived from a fuel supplied to the cell, directly into electrical energy by oxidation of fuel in the cell. These cells are well known to those skilled in the art and are described, e.g., in U.S. Pat. No. 4,988,583 of Watkins et al., U.S. Pat. No. 4,997,726 of Akiyama et al., U.S. Pat. No. 4,981,763 of Mitsuda et al., U.S. Pat. No. 5,026,601 of Iio et al., U.S. Pat. No. 5,021,304 of Ruka et al., U.S. Pat. No. 4,988,582 of Dyer, U.S. Pat. No. 5,035,961 of Riley, and U.S. Pat. No. 4,863,813 of Dyer. The disclosure of each of these United States patents is hereby incorporated by reference into this specification.
Electrochromic devices are also well known. These devices typically are comprised of thin layers of inorganic oxides that change color upon the application of an electric field, maintain the changed condition after the field is turned off, and return to the original state after pole reversal. See, for example, U.S. Pat. No. 4,852,979 of Agrawal as well as U.S. Pat. Nos. 3,712,710, 3,844,636, and 4,465,339. The disclosure of each of these patents is hereby incorporated by reference into this specification.
Both fuel cells and electrochromic cells are electrochemical devices which are comprised of a multiplicity of layers.
One preferred class of such electrochemical devices is the solid devices, such as solid fuel cells, and solid electrochromic cells. These solid devices are often prepared by coating a substrate to produce two or more of the layers used in the structure.
To the best of applicant's knowledge, an economical, reliable process for the large-scale production of high-quality coated electrochemical cell structures has not been provided by the prior art. Thus, by way of illustration, in a publication entitled "Fuel Cells: A Handbook (publication DOE/METC-88/6096 [DE88010252], which was published by the United States Department of Energy, Office of Fossil Energy, Morgantown Energy Technology Center, Morgantown, W.V., in 1988), the disadvantages of electrochemical vapor deposition ("EVD") prior art coating process were discussed. At page 95 of this publication, it is disclosed that "Electrochemical vapor deposition (EVD) presents several limitations in the fabrication of cell interconnections: (a)limited choice of dopants (only Mg has been successfully utilized in Mg-doped lanthanum chromite); (b)non-uniform film thicknesses are deposited; (c)non-uniform dopant concentrations are obtained; and (d)impurities from the gas phase are deposited which may affect the conductivity of the film."
The prior art "EVD" coating process is relatively complicated and, thus, relatively expensive. Thus, at page 597 of A. J. Apleby et al.'s "Fuel Cell Handbook" (Van Nostrand Reinhold, New York, 1989), it is disclosed that this prior art process ". . . involves many complex steps." Thus, e.g., at pages 594-595 of Apleby's book, it is stated that, in the EVD process, ". . .an equimolar mixture of hydrogen gas and water vapor is passed through the porous support tube. . .under low pressure conditions, while the appropriate metal chloride vapors surround the outside of the tube. . .The delivery rate of the metal chloride is controlled by regulating the flow of chlorine over a mixture of granular oxide-lampblack mixture."
On Dec. 20, 1991, the Gas Research Institute of Chicago, Ill. issued a Request for Proposal #92-260-0419, entitled "Intermediate Temperature. . .Planar, Ceramic Electrolyte Fuel Cell Structures." At page 5 of the Request, it was indicated that "A key technical challenge in the fabrication of robust, durable, gas-tight, thin-film structures that operate in aggressive. . .gaseous environments." These structures had not been provided by the prior art.
It is an object of this invention to provide a process for preparing ". . . robust, durable, gas-tight, thin-film structures that operate in aggressive. . .gaseous environments" and which can be used in fuel cells.
It is another object of this invention to provide a process for preparing ". . . robust, durable,. . .thin-film structures that operate in aggressive. . .environments" and which can be used in electrochromic cells.
It is yet another object of this invention to provide a coating process which can be conducted under atmospheric conditions.
It is yet another object of this invention to provide a coating process which produces a coated substrate which is substantially homogeneous.
It is yet another object of this invention to provide a coating process which does not require that the substrate used in the process be heated.
It is yet another object of this invention to provide a coating process which does not require that the coating applied to the substrate material be annealed after deposition.
It is yet another object of this invention to provide a process for the production of coatings which is suitable for the large-scale production of such coatings.
It is yet another object of this invention to provide a process for the production of coatings which can be used to produce complex, coated shaped articles.